A Structured Approach for Optimizing 4-Bit Carry-Lookahead Adder

Abstract

This paper presents a comparative research of low-power and high-speed 4-bit full adder circuits. The representative adders used are a ripple carry adder (RCA) and a carry-lookahead adder (CLA). We also design a proposed carrylookahead adder (PCLA) using a new method that uses NAND gate for modification which helps in reducing the powerdelay product (PDP) for high performance applications. To yield more realistic rise and fall times in the simulations, layouts have been made in a 0.13 􀀁m process for the RCA circuit, CLA circuit and PCLA circuit. The layouts designed were simulated by HSPICE based on 130 nm CMOS technology at 1.2 V supply voltages. Four sets of frequencies were operated: 10 MHz, 50 MHz, 100 MHz and 500 MHz with 50% duty cycle in different technology corner models. A comprehensive comparison and analysis were also carried out to test the performance of the adders. The three adders also yield different performances in terms of power consumption, PDP, and area. The simulation results of this research are expected to help designers to select the appropriate 4-bit adder cell that meets their specific applications.

Wide word‐length carry‐select adder design using ripple carry and carry look‐ahead method based hybrid 4‐bit carry generator

“…To design a wide word-length fast adder, numerous research works have used a 4-bit carry generator as a basic cell. [17][18][19] As a result, the performance of a fast wide word-length adder is highly dependent on its 4-bit fundamental unit cell. Thus, overall improvement of a wide word-length adder structure can be realized by using efficient 4-bit unit cells.…”

“…After that, over the course of time, several CLA designs have been proposed by researchers in order to cope with the rapidly changing technologies. To design a wide word‐length fast adder, numerous research works have used a 4‐bit carry generator as a basic cell 17–19 . As a result, the performance of a fast wide word‐length adder is highly dependent on its 4‐bit fundamental unit cell.…”